1. Field of the Invention
The present invention relates generally to systems and methods for reducing power dissipation requirements and power consumed by single microelectronic devices, and more particularly, to dynamic control of power consumption by and resultant power dissipation required of such microelectronic devices.
2. Background Art
Power dissipation requirements of microelectronic devices (also called semiconductor devices or semiconductor chips or integrated circuits) have become critical in their design, fabrication and use. This is particularly true with very large scale integrated (VLSI) devices and ultra large scale integrated (ULSI) devices, which typically today have over 1,000,000 transistors (active passive) on a single semiconductor die. The active devices are typically run (clocked) at very high speed (25 MHz and 33 MHz speeds are now typical, with much higher clock rates contemplated, for example, 250 MHz) in order to achieve desired system functionality and performance.
As is well known, the high clock rate and the high number of active devices, regardless of the fabrication technology that is used, produce significant power dissipation requirements when compared to the actual physical size of the die of the microelectronic device. For purposes of illustration, a typical die with 1,000,000 active devices is fabricated on a die 15 mm by 15 mm and requires greater than 132 pinouts. Such a microelectronic device can operate at a system clock speed of 30 MHz with 1 micrometer (xcexcm) CMOS technology.
The die must be permanently housed in a suitable housing or package, which among other things (pin out, environmental, physical protection, etc.) must provide adequate heat dissipation in order to prevent failure of the device.
It is not uncommon for a single microelectronic device such as the example above to generate in the range of 5-10 watts of heat that must be dissipated during normal operation. As a result, the junction temperature of the die of such a microelectronic device can reach 100xc2x0 C. for a ceramic package without heatsinking, at the high end of the commercial temperature range, 70xc2x0 ambient. The 5-10 watt number will look small compared to the dissipation requirement for successive generations of more powerful microelectronic devices, which are projected by year 2000 to have 100 million active devices on a single die. Contemplated die sizes are 25 mm by 25 mm.
Various strategies for packaging have evolved to deal with large heat dissipation. All include some type of heat sink or thermal grease arrangement for rapidly drawing away the unwanted heat so as to protect the microelectronic device (die and bond wires) from physical failure and performance degradation. Gas, such as air, and even liquid, such as water, freon, and more efficient coolants are typically used in addition to a conventional heat sink. Heat sink approaches, however, act to increase physical size, cost, mechanical complexity, and weight of the packaged microelectronic device. Moreover, the heat dissipation (i.e., thermal stress) requirements act to limit the physical size of a die that can be accommodated in a single package.
Representative of the heat dissipation requirements are conventional microcrocessor chips running at clock speeds up to 50 MHz, which can typically generate 5 watts of dissipated power in normal operation. In order to accommodate the heat dissipation requirement, special heat sinks arrangement are provided.
The constant trend in electronics is to reduce the size of microelectronic devices so that smaller and lighter electronic and computer products can be made. This miniaturization drive goes on unabated, and historically produces from year to year dramatic reductions in physical size.
The heat dissipation requirement, however, acts as a barrier to this miniaturization process of electronic and computer devices. In other words, the physics of having to dissipate the heat from the microelectronic device limits the physical size and weight reduction of the electronic or computer device that can be achieved. This affects the lifetime of microelectronic devices as well. For example, the reason why a solid state laser has a shorter lifetime than an LED is due to concentration of heat at a small area.
Another significant ongoing trend in electronics is the increase in the features and functions and the decrease in response time that can be provided by an electronic or computer device. This is achieved through more complex and powerful microelectronic devices. This is the result of the increased integration of active devices on a single die. However, additional active devices on the die results in increased heat dissipation requirements, which acts to limit the reduction in the size of the microelectronic device package that can be achieved. Even by reducing the power supply voltage, DEC""s Alpha CMOS chip, for example, is reported to dissipate 30 watts at 200 Mhz.
The dramatic decrease in the physical size of microelectronic devices when compared to their computational capability, and features and functions that they can produce, has resulted in the creation of very small personal computers, typically called laptop, notebook and palmtop computers. This is the latest benchmark in an ongoing trend to reduce in size computers having powerful features and functions.
A typical portable computer today having a 386SX type microprocessor has physical dimensions of 12 in. by 16 in., and a weight of 15 lbs., of which 1 lb. is the rechargeable battery. A typical laptop computer today having a 386SXL type microprocessor has physical dimensions of 8 in. by 11 in. by 2 in. and a weight of 5-7 lbs., of which 0.5 lbs. is the rechargeable battery.
One of the most critical limiting factors, however, to such notebook (also laptop and palmtop) computers is the battery that is needed to run the machine. The battery must provide sufficient electrical power so that the computer can operate for a long enough period of time to satisfy user demand. Typical operating time for notebook computers today is in the range of 3 to 4 hours for a single battery charge.
The battery comprises one of the largest components of the computer system in terms of weight and physical size. However, it is critical for the user that enough electrical power be provided by the battery so that desired computer operation can occur over a sufficient period of time. However, this requirement for operability causes the total size of the computer system to increase since the battery physical size must be increased to meet these requirements.
Consequently, considerable research and development is being directed towards producing much more efficient batteries for a given size and weight. The goal here is to increase battery technology in charge capacity so that the resultant battery will provide more power and longer time for the given size and space. This will in turn act to reduce the size of the computer system that uses it.
In addition to reducing the size of the battery, considerable effort is being expended to try to increase the performance of the computer system in terms of power consumption. One conventional approach as utilized by Intel is to turn off unused peripheral chips. This occurs in the Intel 80386 chip set. By turning off unused peripheral chips, significant battery life can be achieved because the peripheral chips consumed considerable amounts of power.
A further approach implemented in AMD""s AM386DXL microprocessor chip is to slow down the clock speed (e.g., from 40-0 MHz) to conserve power.
In view of the above, there is a great need for improvement in heat dissipation and power consumption by microelectronic devices, particularly used with computer systems, so as to reduce packaging complexity and size and to increase operability time of systems where batteries are used to electronically power the microelectronic devices.
A microelectronic device according to the present invention is made up of two or more functional units, which are all disposed on a single chip, or die. The present invention works on the strategy that all of the functional units on the die are not, and do not need to be operational at a given time in the execution of a computer program that is controlling the microelectronic device. The present invention on a very rapid basis (typically a half clock cycle), therefore, turns on and off the functional units of the microelectronic device in accordance with the requirements of the program being executed. The operation of the present invention results in a very significant reduction in power consumption and corresponding heat dissipation by the microelectronic device as compared to the conventional approach of keeping all functional units operational all of the time.
A representative example of the present invention described herein has achieved a reduction in power dissipation and power consumption of 30% as compared to the normal conventional approach of keeping all of the functional operational units active all of the time during the execution of the computer program. Depending on the architecture of the microelectronic device and the computer program that is being executed, reductions of 0% to 50% can be achieved. Where a single scalar CPU would be on the lower side in comparison to a superscalar CPU architecture, because more blocks may remain idle more frequently.
If the functional units are divided into still smaller blocks, then a higher percentage of units/blocks can be turned off, given that the necessary control logic necessary to perform the switching does not add too much overhead.
The present invention utilizes several approaches for determining when to turn on and off the functional units of the microelectronic device. One approach utilizes the compiler which compiles the source code of the computer program into machine code used to control the operation of the microelectronic device. A logic unit evaluates (e.g., decodes or monitors) the machine code during execution, and based on utilization information provided by the compiler, determines at each step in the execution of the computer program which functional units are needed for execution, and therefore should be turned on or off. For example, a graphics unit may not need to run when non-graphic operations are executing. Similarly, floating point units (FPU) only run 20-30% of the time in a conventional workstation, thus, it does not need to be on during idle periods. Cache memory units also lend themselves to control based on the present invention.
Another approach used by the present invention for determining when to turn on and off the functional units is that performed using a logic unit on the die that evaluates (monitors) the execution and operation of the functional units. This monitoring function produces indications of upcoming operation (including execution and latency to complete the issued instruction) that can be used for controlling the turn on/turn off operation of the present invention. In a compact on-chip low cost FPU, for example, not all the units can be used at the same time or a collision can result. When an FALU operation is being executed, the multiplier or divider may not be pemitted to run. Power can therefore be shut off to these units.
Any suitable preselected amount of time can be used by the present invention for turning on and for turning off the functional units in accordance with the requirements of the computer program that is being executed. The turn on/turn off can be as fast as a half-clock cycle, if desired, so as to produce maximum power dissipation saving and power consumption reduction. Other clock cycle periods for turn on and for turn off can be used. Another method is turning on and off power line(s) to a selected block or blocks.
The present invention contemplates any appropriate electronic approach for turning on and off a functional unit. In complementary metal oxide semiconductor (CMOS) circuits, a preferred approach is either (1) to stop the clock signal to the functional unit that is being turned off, or (2) to stop the inputs of the functional unit being turned off from changing. Either approach produces the desired result of turning off the functional unit The functional unit can be subsequently turned on by the opposite approach that is used for turning it off.
The present invention has particular applicability to CMOS circuitry because it takes full advantage of the CMOS characteristic that no power is consumed by a circuit unless there is a state change. By preventing state changes in the functional unit(s) not being used at that point in the execution of the computer program, the present invention can produce the desired power dissipation requirement reduction and power consumption reduction. Switching the power buses on/off is not necessary, and minimal chip area is required for control.